Micropaleontological observations on the Lower Cretaceous iron ore-related formations of the Mecsek Mts. (Upper Valanginian–Lower Hauterivian, South Hungary)

Abstract

The Late Valanginian-Early Hauterivian iron ore deposit and related formations at Zengővárkony (Mecsek Mts., South Hungary) provided a relatively rich microfauna of foraminifera, crustacean microcoprolites, and sponge spicules. Benthic foraminifera are recognized in decreasing abundance: Glomospira cf. gordialis (Jones and Parker 1860), Lenticulina sp., Spirillina sp., Nodosaria sp., Epistomina sp., and Trocholina sp. A Hedbergella sp. indicates the presence of planktonic foraminifera around the ore deposit. Besides this microfauna, sponge spicules (diactine-type criccorhabds and anactine-type rhax forms) are first recorded from this environment. Rock-forming quantities of various ichnospecies of crustacean microcoprolites are recorded. Favreina hexaochetarius, Palaxius tetraochetarius, and Palaxius decaochetarius isp. provided statistically evaluated quantities in thin sections, which point to a complete crustacean ichnofauna from juveniles to adults. Four different microfossil assemblages are recognized from the Apátvarasd Limestone Fm: (a) Glomospira-dominated foraminifer assemblage, (b) diverse crustacean microcoprolite assemblage dominated by Palaxius, (c) monotypic Favreina assemblage, and (d) diverse sponge-dominated assemblage. These assemblages are similar to that of the Recent Aegean Sea hydrothermal field communities. The remains of an undetermined crinoid from dissolved rock sample may indicate a vivid sea-bottom environment.

New kingenoid (Terebratellidina) brachiopods with larger body sizes from the Early Cretaceous of Zengővárkony (Mecsek Mountains, Hungary)

“…The intercalating and metasomatized limestone bed provided a rich foraminiferan assemblage of Glomospira spp., Lenticulina spp., Spirillina spp., Nodosaria spp., Epistomina spp., Trocholina spp., and Hedbergella spp. (Bujtor and Szinger, 2018). The fossil content decreases upward in number of individuals and diversity: toward the top of the section, only badly preserved echinoid spines are present.…”

“…Submarine volcanic bodies were reported from other places in the eastern Mecsek Mountains and have been thoroughly investigated (Mauritz, 1913, 1958; Bilik, 1974, 1983). Simultaneously with the volcanism, a sedimentary iron ore body was deposited (Sztrókay, 1952; Pantó et al, 1955; Molnár, 1961) southeast of the volcanic center that hosted a rich marine fauna (Fülöp in Hetényi et al, 1968; Bujtor, 2006, 2007; Bujtor and Szinger, 2018; Bujtor et al, 2013).

Figure 2.Palaeogeographic position of the Tisza Mega-Unit microplate including the Mecsek Mountains in the earliest Cretaceous.

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“…The section (Fig. 3) is an artificial cut prepared for fossil collecting on the western slope of the Dezső Rezső Valley reported in detail by Bujtor (2006, 2007, 2012b), Bujtor and Szinger (2018), and Bujtor et al (2013). The section traverses the volcano-sedimentary succession of the Mecsekjános Basalt Formation and the overlying Apátvarasd Limestone Formation.…”

“…Thin sections (Fig. 4) of ammonite body chambers reveal microfaunal elements, such as foraminiferans, echinoderm remains, sponge spicules, and rarely crustacean microcoprolites (Bujtor, 2012b; Bujtor and Szinger, 2018). The intercalating and metasomatized limestone bed provided a rich foraminiferan assemblage of Glomospira spp., Lenticulina spp., Spirillina spp., Nodosaria spp., Epistomina spp., Trocholina spp., and Hedbergella spp.…”

“…Based on dinoflagellates and belemnites, the age of the fossiliferous layers is upper Valanginian–lower Hauterivian, which strengthens the conclusions of Fülöp (in Hetényi et al, 1968). Regarding the microfauna, Bujtor and Szinger (2018) described diactine-type criccorhabd sponge spicules from the same locality. During serial sectioning of the present material, sponge spicules also appeared frequently inside the brachiopod shells.…”